1. Field of the Invention
The present invention relates to an oriented polymer composition and a process for preparing the oriented polymer composition.
2. Description of Related Art
Oriented polymer compositions (OPCs) are gaining market share in construction markets previously occupied almost solely by wood materials. For example, a number of different OPC decking materials are now available for use instead of cedar, redwood, treated pine, or other more historically standard decking materials.
OPCs are particularly desirable for construction applications. Orienting a polymer composition strengthens the polymer composition by aligning polymer chains in a particular direction. As a result, the flexural modulus of the polymer composition increases, which is desirable in load bearing applications common in construction.
Tensile drawing processes for preparing OPCs can also advantageously induce cavitation during orientation. Cavitation is desirable to reduce OPC density to facilitate shipping and handling of the OPC as well as overall structure weight for structures containing the OPC.
While these attractive features tend to make OPCs more desirable than non-oriented polymer composition, OPCs also have their drawbacks over non-oriented polymer compositions. OPCs can suffer from fibrillation along their orientation direction as groups of aligned polymer chains peel away from neighboring aligned polymers. Fibrillation can be apparent upon scuffing or cutting OPCs transverse to their orientation direction. Therefore, OPCs are desirable for their high flexural modulus, but can have durability problems in regards to fibrillation.
U.S. Pat. No. 5,204,045 ('045) addresses the problem of fibrillation in OPCs by creating an OPC that has a skin of low orientation and a core of higher orientation. The low orientation skin provides integrity lacking in OPCs while the highly oriented core provides a desirable flexural modulus. '045 describes preparing OPCs using a ram extrusion method wherein an orientable polymer composition is pushed through a converging die while maintaining the die at a temperature high enough to melt a polymer skin on the surface of the polymer composition. The resulting OPC has an oriented core and a non-oriented skin directly upon orientation. Ram extrusion methods require application of compressive force rather than tensile force and so cavitation in order to reduce OPC density is not possible. Still more, ram extrusion processes are batch processes as opposed to continuous processes.
It is desirable to find an alternative way to prepare unique OPCs that offers a combination of the high flexural modulus of an OPC with the structural integrity against surface fibrillation of a non-oriented polymer composition and that desirable utilize tensile force, achieves cavitation, is continuous, or any combination of these desirable features. It is also desirable to be able to convert an OPC that has an oriented surface to one that has an oriented core but a de-oriented surface. It can be further desirable to have the option of de-orienting a surface of an OPC while leaving other surfaces oriented in order to, for example, maximize OPC strength by retaining as much orientation as possible while improving cutability on a particular surface.